Re: Questions on XDP

On Sat, 2017-02-18 at 17:34 +0100, Jesper Dangaard Brouer wrote:

On Thu, 16 Feb 2017 14:36:41 -0800
John Fastabend [off-list ref] wrote:

quoted

On 17-02-16 12:41 PM, Alexander Duyck wrote:

quoted

So I'm in the process of working on enabling XDP for the Intel NICs
and I had a few questions so I just thought I would put them out here
to try and get everything sorted before I paint myself into a corner.
  
So my first question is why does the documentation mention 1 frame per
page for XDP?  

Yes, XDP defines upfront a memory model where there is only one packet
per page[1], please respect that!

This is currently used/needed for fast-direct recycling of pages inside
the driver for XDP_DROP and XDP_TX, _without_ performing any atomic
refcnt operations on the page. E.g. see mlx4_en_rx_recycle().

XDP_DROP does not require having one page per frame.

(Look after my recent mlx4 patch series if you need to be convinced)

Only XDP_TX is.

This requirement makes XDP useless (very OOM likely) on arches with 64K
pages.